Type 2 diabetes increases the risk for developing breast cancer in postmenopausal women. Epidemiological studies have recently revealed that the glucose-lowering drug, metformin, reduces breast cancer in women with diabetes. We recently reported that the flavanoid, naringenin acts like metformin to lower glucose production by hepatocytes. Naringenin is surfacing as a chemopreventive agent in several preclinical models for cancer. Since the bioavailability, tissue accumulation and biological activity of dietar naringenin in mammary gland have not been reported, we propose to quantify the accumulation of naringenin in mammary tissues and blood then determine the ability of dietary naringenin to modulate growth of mammary tumors in obese female mice. There are three aims of this study. In Aim 1, we will test the hypothesis that increasing doses of dietary naringenin result in a dose- responsive accumulation of naringenin in blood and tissues without detrimental effects on food intake and weight gain. In Aim 2, we will test the hypothesis that naringenin reduces the rate of growth of tumors. In Aim 3, we will test the hypothesis that dietary naringenin modulates signaling events involved with tumorigenesis and metabolism. Accomplishment of the experiments outlined in this proposal will determine whether there is rationale for future experiments to identify dietary naringenin as a preventive agent against breast cancer.